TYPES AND MECHANISMS · Common name Scientific name Cultivar Cotton American bollworm Helicoverpa armigera Sujata,Abadhita, Sujay Pink bollworm Pectinophora gossypiella LD135, Sujata,

Course teacherDr. A. Prabhuraj

ProfessorDepartment of Entomology

UAS, Raichur

TYPES AND MECHANISMS

MECHANISM OF RESISTANCE

Antixenosis

Antibiosis

Tolerance

Three fold basis Resistance based insect plant interaction according to Painter

(1951) is

Antixenosis(Pest reaction)

Antibiosis

(Plant reaction)

Tolerance(Reaction of both)

I

N

S

E

T

P

L

A

N

T

Antixenosis (Non acceptance)

Xeno- meaning guestType of resistance where insect will not accept for feeding & breeding even if there is no alternative source.

Ø Host plant characters responsible for non-preference of theinsects for shelter, oviposition, feeding, etc.

Ø It denotes presence of morphological or chemcial factorwhich alter insect behaviour resulting in poor establishmentof the insect

ANTIXENOSIS

PLANT DEFENCES IMPARTING

ANTIXENOSIS

OLFACTION

VISION

THIGMORECEPTION

GUSTATION

PLANT DEFENCES AFFECTING INSECT

BEHAVIOUR

TRICHOMES

SURFACE WAXES

TISSUE THICKNESS

ANTIXENOSIS

Mechanisms of ResistanceThe three important mechanisms of resistance are- Antixenosis (Non preference)- Antibiosis- Tolerance

Open panicle of sorghum - Supports less Helicoverpa

Examples for antixenosis

Trichomes in cotton - resistant to whitefly Wax bloom on crucifer leaves - deter feeding by DBM

Plant shape and colour also play a role in non preference

Insect pests Host plant charactersNon-preference Preference

Bollworms Smooth leaves Hairy leavesNectarileness NectarineLong pedicel Short pedicelThick boll rind Thin boll rindOkra leaf Soft boll rind

Boll weevil Frego bract Normal bractRed plant body Green plant bodyHairy leaves Smooth leavesLeathery leaves Succulent leaves

Whitefly Smooth leaves Hairy leavesThin leaves Normal leaves

Table 1. Important non preference characters

ANTIBIOSIS• Adverse effect of the host plant on the biology (survival,

development and reproduction) of the insects and their progeny due to the biochemical and biophysical factors present in it

• It may be due to :a. Presence of toxic substances-b. Absence of sufficient amount of essential nutrientsc. Nutrient imbalance/improper utilization of nutrients

Chemical means Physical means DIMBOA (Dihydroxy methyl benzoxazin) against European cornborer

Thick cuticle

Gossypol against American bollworm

Glandular hairs

Sinigrin against Aphids Silica depositsCucurbitacin against Myzus persicae Tight leaf sheath

ANTI BIOSIS

PLANT DEFENSES INMPARTING ANTIBIOSIS

ALLELO-CHEMICALS

GROWTHINHIBITORS

MORPHOLOGICAL

BARRIERS

TOLERANCE

QUANTITATIVE MEASURMENT

OF TOLERANCE

FACTORS AFFECTING EXPRESSION

OF TOLERANCE

- The effects may be

Direct

1) Growth 2) Development

3) Reproduction 4) Survival

5) General vigour

Indirect

1) Vulnerability to biocontrol agents

2) Vulnerability to environmental aberration

- Overal all effect is reduction in rate of population increase

- Often mechanisms of antixenosis and antibiosis overlap

Toxins of Plant origin

• Lectin• Lectin phytoheamaglutinin• Wheat germ agglutinin

Enzymes & Enzyme inhibitors• Protease inhibitors• Trypsin inhibitors• Alpha amylase inhibitors

• Snowdrop lectin, Galanthusnivalis Sucking pests, Pulse beetle and storage pests

• Leguminacea• Solanaceae• Poaceae

Components Confer resistance

High gossypol Bollworms, tobacco budworm and red spider mite

High phenol Bollworms

High condensed tannin

Bollworms, aphids, lygus bugs, red spider mites and leaf miners

High tannin

In leaves Jassids

In buds Bollworm tolerance

Low sugar

In anther Boll weevil and bollworms

Table 2. Biochemical components

Jenkins, 1994 (USA)

Tolerance § Ability of the plant to grow and reproduce and even repair

injury to a marked degree inspite of supporting a population approximately equal to that damaging a susceptible host

§ Plant is damaged but there is no economic yield loss or lowering of quality

§ Often tolerance is confused with low level of resistance or moderate resistance

§ It totally different from other two causes by not coming in/on to the way of insect activity

§ Therefore, it may be regarded as susceptible based on insect

number or damage

§ It is an adaptive mechanism for the survival of plant and is

more or less independent of the effect upon the insect

§ This type of resistance refers strictly to resultant effects and

not to mechanisms.

Common name Scientific name CultivarCottonAmerican bollworm Helicoverpa armigera Sujata, Abadhita, SujayPink bollworm Pectinophora gossypiella LD135, Sujata, AbadhitaSpotted bollworm Earias vittella LD1245, SanguineumCotton jassid Amarsca bigutulla Mahalaxmi, SujaySugarcaneInternode borer Chilo sacchariphagus indicus Co6806, Co975Top borer Scirpophaga exercerptalis Co7224, Co1158White grubs Holotrichia spp. Co6304, Co5510MaizeMaize shoot fly Atherigona sp. DMR5, VC80Pink stem borer Sesamia innferens Deccan 101 and 103RiceBrown plant hopper Nilaparvata lugens IET7575, JyotiGall midge Oaseolia virens Phalguna, IR36Yellow stem borer Scirpophaga incertulas Ratna, MTU5849

Insect-resistant cultivar developed for different crops in India

GroundnutLeaf miner Aproaerema modicella ICGV86031, ICG57Tobacco leaf caterpillar Spodoptera litura ICGV86031, FDRS 10SoyabeanLeaf miner Aproaerema modicella Nimsoy, PL507Chick peaPod borer Helicoverpa armigera Anupani, ICCV10, DuliaPigeon peaPod borer Helicoverpa armigera Bori, ICPL332, BSMR 1BrinjalShoot and fruit borer Leucinodes orbonalis Pusa purple long, SM68Jassid Empoasca kerri Krishna, UPB 1PotatoPotato tuber moth Phthorimaea operculella QB 1A 21-29TomatoFruit borer Helicoverpa armigera Pant bahar, BT 1, T 32

A. Advantages of host plant resistance

Ø Cumulative and persistent

Ø No additional cost to grower (other than purchasing seed resistant to pests.

Ø No harmful residues

Ø No damage to beneficial fauna

Ø Integrates effectively with other control methods

Ø Conserves bio-control agents

Ø Most useful in low economic crops.

B. Primary disadvantages of host plant resistance

Ø Several years to develop for one pest, longer for multiple resistance

Ø Different varieties needed for different geographical areasØ Need for good agronomic quality along with resistanceØ Resistance most offen found in species of off types of poor

agronomic quality require much time to develop to an acceptant variety

Ø Biotypes. Insects adapt or change so as to feed on formerly resistant plants

Ø Incompatibility of resistance character with other charactersØ Replacement of varieties by better yielders

Compatibility of HPR in IPM

a. Compatibility with chemical controlØHPR enhances efficacy of insecticidesØHigher mortality of leaf hoppers and plant hoppers in resistant variety compared to

susceptible varietyØLower concentration of insecticide is sufficient to control insects on resistant variety

b. Compatibility with biological controlØ Resistant varieties reduce pest numbers - thus shifting pest: Predatory (or

parasitoid) ratio favourable for biological control. e.g. Predatory activity of miridbug Cyrtorhinus lividipennis on BPH was more on a resistant rice variety IR 36than susceptible variety IR 8ØInsects feeding on resistant varieties are more susceptible to virus disease (NPV)

c. Compatibility with cultural methodØCultural practices can help in better utilization of resistant varieties. e.g. Use of

short duration, pest resistant plants effective against cotton boll weevil in USA.

Advantages of HPR as a component in IPM

Ø Specificity: Specific to the target pest. Natural enemies unaffectedØ Cumulative effect: Lasts for many successive generationsØ Eco-friendly: No pollution. No effect on man and animalsØ Easily adoptable: High yielding insect resistant variety easily accepted and adopted by

farmers. Less cost.Ø Effectiveness: Res. variety increases efficacy of insecticides and natural enemiesØ Compatability: HPR can be combined with all other components of IPMØ Decreased pesticide application: Resistant varieties requires less frequent and low doses

of insecticidesØ Persistence: Some varieties have durable resistance for long periodsØ Unique situations: HPR effective where other control measures are less effective

e.g. a. When timing of application is criticalb. Crop of low economic valuec. Pest is continuously present and is a single limiting factor

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